Our recent serological work on embryonal carcinoma cells and embryos carrying mutant genes at the T/t locus has provided evidence that changes in cell surface antigens occur as development proceeds, and that abnormal surface components can be responsible for abnormal forms of embryonic differentiation that may result in malignancy. In this project we intend to begin to examine the molecular nature of cell membrane-associated molecules that may play a role in mediating morphogenetic events. Carbohydrate-containing components and glycosyltransferases at the cell surface have both been theoretically implicated in cell recognition and cell interactions. We plan therefore to compare cells of three types, namely normal embryonic cells, teratocarcinoma cells, and mutant embryonic cells whose differentiation is blocked, with respect to cell surface representation of these components. These three cells types will be compared with respect to: (1) their binding capacity for a battery of specific lectins; (2) the topology of lectin binding; (3) their representation of membrane-bound glycosyltransferases, and (4) their plasmalemmal content of glycoproteins. This should enable us to define differences between normal embryonic cells and embryonic cells that are abnormal either because of malignancy or mutational effects that interfere with differentiation. This is a first step toward identifying molecules at the cell surface that are crucial for cell interactions.